Overview
Bonding Ionic Covalent MetallicStructure Giant
ionicSimple
molecularGiant
covalentGiant
MetallicExample Sodium
chlorideWater Diamond Iron
Bonding and structure explains the properties of a substance!
Physical & Chemical Properties
‘property’: ‘what something is like’ Physical properties of a substance are those that
can be observed or measured without the substance changing into another substance.
Chemical properties of a substance describe the change of a substance into another substance.
Some examples of physical properties:Melting and
boiling pointsElectrical
conductivitySolubility in water (or other solvents)
Ionic Bond: The Definition
An ionic bond… is the force of attraction between
opppositely charged ions in a compound.
Giant Ionic StructuresPhysical Properties: M.P. & B.P.
Ionic compounds have high melting and boiling points.
strong electrostatic forces of attraction between the ions in an ionic compound
large amount of heat is needed to break the strong ionic bonds holding the ions together
Giant Ionic StructuresPhysical Properties: Electrical Conductivity
Ionic compounds do not conduct electricity in the solid state. It conducts electricity
in the molten and aqueous state.
Why do ionic compounds only conduct electricity in the molten or aqueous state, but not in the solid state?
ions can move in the molten or aqueous state moving ions carry the electric current
Giant Ionic Structures Physical Properties: Solubility
Ionic compounds are soluble in water but insoluble in organic solvents.
ions attract water molecules disrupts the crystal structure cause the ions to separate and go into solution
Giant Ionic StructuresPhysical Properties: Volatility
Ionic compounds are not volatile and hence, have no smell.
cannot evaporate easily because of strong ionic bonds holding the ions together
A volatile substance evaporates easily.
Giant Ionic StructuresPhysical Properties: Physical State
Ionic compounds are hard, crystalline solids. ions held in place by strong ionic bonds, make the
crystal hard ions are arranged in straight rows and form
structure with flat sides, resulting in a crystalline structure (flat sides & regular shapes)
Ionic VS Covalent
Similarities Electronic configuration of a noble gas
(PS: Everybody wants to be noble!!)
Differences
Ionic Bond Covalent BondBetween positive ions of metals and negative ions of non-metals
Between non-metal atoms
Electrons are transferred Electrons are shared
Covalent Bond: The Definition
A covalent bond is…
a bond formed by the sharing of a pair of electrons.
More about COVALENT BONDING
Each atom acquires a stable octet structure Electronic configuration of noble gas (Full shell) =
Energetically stable
Formed between atoms of non-metals (but there are exceptions!) “Spectrum” of bonds
Simple Molecular Substances
Within the moleculeAtoms are held together by strong covalent bonds
Between moleculesWeak intermolecular forces (van der Waals’ forces)
Iodine, I2
Within each iodine molecule, the iodine atoms are held together by strong covalent bonds.
Between the iodine molecules, there are only weak van der Waals’ forces holding the molecules together.
Methane, CH4
In a molecule of methane, CH4, the four C–H covalent bonds are strong.
However, weak intermolecular forces between methane molecules hold them together loosely. Therefore, methane exists as a gas at room temperature and pressure.
Physical Properties
Physical state Most substances are liquids or gases at
room temperature. Forces between molecules are weak,
allowing molecules to move freely.
Low M.P. & B.P. Little energy required
to overcome the (weak) intermolecular forces
(Usually <200°C)
Melting & Boiling Points
Covalent substance Melting point (C) Boiling point (C)
Carbon dioxide -56 -79
Chlorine -101 -35
Hydrogen -259 -253
Methane -183 -161
Oxygen -214 -183
Water 0 100
Physical Properties
Volatility Low B.P. = Volatile Evaporate easily (to give a smell)
Electrical conductivity Do not conduct electricity. (Some exceptions, e.g. graphite) No free-moving ions or electrons to conduct electricity
Solubility Most molecular substances are insoluble in water, but
dissolve in organic solvents. (Some exceptions, e.g. alcohol and sugar, hydrogen chloride)